[FAB-12464] fix query retries for MVCC Conflicts

	The CI complains for Discovery Server failing to read
	private data. Need to make sure Discovery Server and
	Endorser Server do retries on MVCC Conflict errors

Change-Id: I4f9b81b9258519df34ab6fee27cc272ad5f7dd25
Signed-off-by: Baha Shaaban <baha.shaaban@securekey.com>

pkg/common/errors/retry/defaults.go

@@ -172,6 +172,7 @@ var TestRetryableCodes = map[status.Group][]status.Code{
 	},
 	status.DiscoveryServerStatus: {
 		status.QueryEndorsers,
+		status.Code(pb.TxValidationCode_MVCC_READ_CONFLICT),
 	},
 	status.EndorserClientStatus: {
 		status.ConnectionFailed, status.EndorsementMismatch,
@@ -183,6 +184,7 @@ var TestRetryableCodes = map[status.Group][]status.Code{
 	status.EndorserServerStatus: {
 		status.Code(common.Status_SERVICE_UNAVAILABLE),
 		status.Code(common.Status_INTERNAL_SERVER_ERROR),
+		status.Code(pb.TxValidationCode_MVCC_READ_CONFLICT),
 	},
 	status.OrdererClientStatus: {
 		status.ConnectionFailed,